GATE Electrical Engineering (EE) 2019 Solved Paper

A co-axial cylindrical capacitor shown in Figure (i) has dielectric with relative permittivity ${\mathit{\epsilon }}_{\mathit{r}\mathit{l}}=2$. When one-fourth portion of the dielectric is replaced with another dielectric of relative permittivity ${\mathit{\epsilon }}_{\mathit{r}2}$, as shown in Figure (ii), the capacitance is doubled. The value of ${\mathit{\epsilon }}_{\mathit{r}2}$ is___________.